In the conversation in which Louisa Mebbin threatens to expose Mrs. Packletide for lying about killing the tiger, the narrator uses both an oxymoron and a simile, as seen in the following passage:
“How amused every one would be if they knew what really happened,” said Louisa Mebbin a few days after the ball.
“What do you mean?” asked Mrs Packletide quickly.
“How you shot the goat and frightened the tiger to death,” said Miss Mebbin, with her disagreeably pleasant laugh.
“No one would believe it,” said Mrs Packletide, her face changing colour as rapidly as though it were going through a book of patterns before post-time.
The oxymoron here—in which the narrator describes Louisa’s “disagreeably pleasant” laugh—communicates that Louisa is knowingly blackmailing Mrs. Packletide while acting as if she is simply having a casual conversation with her employer. The negative connotation of “disagreeably” plus the positive connotation of “pleasant” hints at the tension between Louisa’s intentions and outward behavior. This sort of dissonance was common in the Edwardian era as middle- and upper-class people would insult or threaten people under the guise of being “polite.”
The simile here—in which the narrator describes how Mrs. Packletide’s face “chang[ed] colour as rapidly as though it were going through a book of patterns before post-time”—captures how flustered Mrs. Packletide is by being subtly blackmailed by her employee. As Saki assumed his early-20th-century readers would know, people who bet on horse races would look through books that contained different horses’ racing patterns, but they only had so long to study them before having to place their bets (by “post-time”). In this way, Mrs. Packletide’s face changing colors communicates her stress and sense that she has been backed into a corner.